Seeing and Perceiving

Modeling the response of photoreceptors Our goal now is to develop a way of making quantitative statements about the response of a photoreceptor to a particular light. To do this, we have to formalize the way we talk about light, the way we describe what a photopigment does, and what happens when the two things interact. So far, we’ve been thinking about these things intuitively, but to go further we have to be much more concrete. Let’s start with formalizing the way we talk about light. We’ve already discussed that there are different kinds of light that differ from one another in terms of their wavelength , which seems to have something to do with color (remember that red and blue light diffracted differently). We also know that light of any wavelength can sometimes be bright and sometimes be faint, this related to the amplitude of light if we’re thinking about light as a wave, and its related to how many light particles (or photons ) there are in a stimulus if we’re thinking...

Observing the retina (and what it can do) Now that we’ve seen how images are formed inside of a pinhole camera, we have a sense of how patterns of light from the environment become patterns of light inside the eye. The next question is how those patterns become signals that can be sent from the eye to the brain. This process is called transduction , and within the eye, the structure that actually transduces light is called the retina . How does this bit of tissue sense light? Something must be happening that turns light into an electrical signal, but what? We’ll develop a quantitative model of how this works, but first, we’ll try to develop a basic understanding of the retina based on some simple observations. Compared to some of our previous discussions, this is going to be a little trickier – the retina is inside our eye, for example, so we can’t just look at the parts of it the way you were able to look at your own pupil. Instead, we’re going to adopt a dual strategy of (1) Makin...

Lab #4 - Observing retinal inhomgeneities Back-to-back lab activities, but there's a method to the madness: In this set of exercises, you'll make a series of observations designed to show off how your ability to see depends on which part of your retina you're trying to see with. Here's a link to the lab document: https://drive.google.com/file/d/1VwIY1bDNF4CI4CUVaY5WSvQ0HxF9Mn6Y/view When you're done here, we're ready to start saying more about the retina and how it works. Our next posts will be all about developing a model that we can use to describe the retina's contribution to your vision quantitatively, so get ready to calculate some stuff!

Lab #3 - Photopigments Our next task is to work out how you translate the image formed in the back of a pinhole camera into some kind of signal that your nervous system can work with. We'll start addressing this question by examining photopigments  in Lab #3. To complete this lab, you'll need access to some sunprint paper, which is available from a variety of different sources. Here's where I bought mine:  http://www.sunprints.org . You can find the lab documents at the link below: https://drive.google.com/file/d/17MVZqvyiCRdT_Qu5n_CtK3rVcUP0zoOG/view When you're done, move on to the Lab #4 post to make a few more observations that will give us a little more information about the retina. Afterwards, we'll try to put all of this together into a more comprehensive description of what's happening at the back of the eye.

How does the eye form images? How does the eye work? Our pinhole camera is a stripped-down version of an eye that only has a few parts for us to play with. Still, changing those parts around a little and observing what we see goes a long way towards helping us understand what the parts of your eye are doing to record patterns of light in your visual world. First, let’s start by reminding ourselves of the things you saw using your pinhole camera. Inverted images in the pinhole camera One of the more conspicuous features of your pinhole camera was that the images produced on the viewing screen in the back were upside-down and backwards. This is a direct consequence of how light gets from the outside world to the viewing screen. Because you sealed your camera up carefully, the only way light can get from an object in the environment to the viewing screen is by passing through the pinhole in the front of the camera. This means that light from the top of a visual scene passes th...